Node Storage

  • NodeStorage is the central concept that defines what a node storage must be able to do.

  • NodeStorageVTable is a vtable for a NodeStorage. It can be generated from any class that is a NodeStorage.

  • DynNodeStoragePtr is a non-owning pointer to any NodeStorage, it stores an instance-pointer and a vtable-pointer.

  • Identifiers for Nodes and their properties are found in Identifiers Used to Store Nodes

  • A reference implementation of a thread-safe node storage backend based on tsl::sparse_map is provided at rdf4cpp::storage::reference_node_storage::ReferenceNodeStorageBackend

  • Backend Views contains proxy classes to access information about a node stored in an implementation-specific backend.

Requirements for NodeStorage Implementations

  • Implementations must not assume that all nodes are stored in the node storage, in fact small Literals that can fit in 42 bits (e.g. values of xsd:int) are usually not stored there

  • IRIs, BlankNodes and Variables should usually be stored as their string representations

  • Literals can be stored either as their canonical lexical form or as values

    • when trying to store Literals as values the implementation is required to accurately report which Literal types can be stored as values via rdf4cpp::storage::NodeStorage::has_specialized_storage_for(). Inaccurate reporting will result in undefined behaviour.

    • Warning: Literals that have value storage are assumed to never need escaping when converting them to their n-triples string representation. I.e. the output of their corresponding to_string function will be used without escaping it.

    • see rdf4cpp::storage::reference_node_storage::SyncReferenceNodeStorage for details

  • Some IRIs are reserved by default (see rdf4cpp::datatypes::registry::reserved_datatype_ids) these IRIs must always be present in the NodeStorage and assigned the given NodeID. Not upholding this invariant results in undefined behaviour. See :class:`rdf4cpp::storage::reference_node_storage::SyncReferenceNodeStorage` for the expected usage.

General Notes for Implementors

  • Passing a `Literal` that is supposed to be stored in lexical storage (as required by the `NodeStorage` implementation) as a value view results in undefined behaviour.

  • Passing a `Literal` that is supposed to be stored in value storage (as required by the `NodeStorage` implementation) as a lexical view results in undefined behaviour.